Video surveillance plays important rules in security systems. Video surveillance may be used in crime prevention, industrial process, traffic monitoring, transport safety, control of retail, etc. Some existing video surveillance techniques detect an object by defining a tripwire in one or more video frames of a video and determining whether the object moves across the tripwire. Although these methods may be easy to implement, there are shortcomings. For example, the existing detection technology may include a tripwire detection and an intrusion detection. The tripwire detection and intrusion detection may identify an event according to a direct determination whether a target intersects with a tripwire. However, an event may not always occur when the target intersects with the tripwire because of the perspective effect of the camera, and thus false alarms may be generated in these circumstances.